The present invention relates to a long twist drill for metal machining.
Deep hole drilling applications can often be found in the automotive, mould & die industries and general engineering. During metal cutting operation chips are produced at the tip end of the shank of the twist drill, said chips being formed and transported from the tip end of the shank of the twist drill to the opposite end of the shank of the twist drill. In metalworking industries there are numerous deep holes produced daily. Deep holes can be defined as being at least 15 times the hole diameter. Drilling tools predominantly used nowadays, such as gun drills and HSS drills usually result in very long process times. In general, drilling becomes more and more difficult with increasing drilling depth. More recent drills have pushed the constraints of tool design further than ever by using a solid carbide twist drill with internal coolant supply to meet the demands of deep hole drilling. The new twist drills can be used for most materials and are very tolerant in terms of the coolant type and feed applied. During rotation the chips are forced out of the hole by a drill helix and chip transport takes place in flutes. This allows the reliable transport of large, jamming chips such as the ones produced by long-chip materials. The chip transport is particularly important when the drilled depth is relatively large compared to the nominal diameter. Twist drills are often coated with a hard material to increase tool life by enhancing the wear resistance. JP 2007276076 discloses a long twist drill. In spite of the recent developments there is a need to further optimize the long twist drills.